This invention relates to a key input device of a capacitance detecting type.
A conventional key input device of the capacitance detecting type includes exposed conductive electrodes which can be touched by fingers of an operator. When an electrode is touched by a finger of the operator, a capacitance related to the electrode is varied. The key input device includes a circuit which functions to detect such a variation in the capacitance. This circuit generates a signal representing whether or not the electrode is touched.
In a prior-art key input device of the capacitance detecting type, as conductive electrodes are close to each other, a touch to one electrode tends to cause a wrong signal representing that a neighboring electrode is touched. Capacitances between the electrodes increase as the electrodes are close to each other. Increased capacitances between the electrodes are a major factor in the causation of such a wrong signal.